It is known to incorporate a load sensor on the output shaft of a drive unit and to use this sensor to operate a clutch to disconnect the output shaft from the input shaft in the event of an overload. German patent specification No. 3043237 (which has an equivalent GB No. 2088442) describes a drive or gearing unit of this type. U.S. patent application Ser. No. 563,487, filed Dec. 20, 1983 and assigned to the same assignee as the present application, desribes a modified protection system in which the response time is minimized. In the known systems, strain gauge transducers are normally mounted directly on rotating shafts and this presents considerable difficulties in the transmission of the electrical signals. Moreover, the operation of removing and replacing the transducers is laborious and time consuming.
A general object of the present invention is to provide an improved gearing unit with overload sensing and protection.